Ventilation devices of the type addressed herein are used in connection with hydraulic actuator chambers, in particular hydraulic cylinders, in order to be able to ventilate the hydraulic actuating circuit in the direction of the tank of the hydraulic medium. The objective is to provide a stable hydraulic line when the actuator is actuated. The said ventilation devices are used, in particular, in dual clutch transmissions, even more particularly in clutch cylinders of dual clutch transmissions. Such clutch cylinders serve to engage or release the clutches of a dual clutch transmission. Preferably, the said ventilation devices can also be used in connection with the gear actuating cylinders of a dual clutch transmission. The ventilation devices known from the prior art have a flow channel that has an inlet and an outlet and passes through the ventilation device. There is a closing element that is pushed typically by the force of gravity into a first functional position, in which the outlet is released. At the same time, the closing element can be entrained by the medium flowing by and can be pushed into a second functional position in which it closes the outlet. If a hydraulic cylinder, assigned to the ventilation device, is ventilated, then the air or rather the expelled gaseous medium flows through the inlet into the ventilation device, past the closing element, and through the outlet out of the ventilation device. The viscosity of the gaseous medium is not adequate enough to entrain the closing element and to push it in a sealing manner against the outlet. As soon as the ventilation process has been completed, the hydraulic medium flows into the inlet of the ventilation device and from there to the outlet. The hydraulic medium exhibits a significantly higher viscosity than the medium expelled during the ventilation process, so that said hydraulic medium can entrain the closing element when it flows around the same. In this way, the closing element is pushed against the outlet and closes it in a sealing manner. An additional increase in the hydraulic pressure pushes the closing element with greater force against the outlet so that the sealing effect increases as the pressure increases. Therefore, no hydraulic medium can flow out through the outlet while the hydraulic cylinder is pressurized.
The drawback with the known ventilation devices is that in the depressurized state of the hydraulic cylinder, that is, in the first functional position of the closing element, both the inlet and the outlet are released. If, therefore, smaller quantities of hydraulic medium were to find their way to the ventilation device, they could escape through the released flow channel. In addition, the closing element, around which the hydraulic medium flows, possesses a certain degree of inertia, so that the hydraulic medium can escape through the outlet before the closing element is reliably pushed into a second functional position. Therefore, the object of the invention is to provide a ventilation device for a hydraulic cylinder, in particular a dual clutch transmission, so that this ventilation device does not exhibit the aforementioned drawbacks.